Reactive dyes are also called reactive dyes. The molecule contains a chemically active group that can react with cotton, wool and other fibers in an aqueous solution to form a co-bonded dye.
Has high washing fastness.
According to different reactive groups, reactive dyes can be divided into two main categories.
Symmetric triazine type The general formula is:
In the formula, D is the parent dye. In this kind of reactive dyes, the chemical nature of the chlorine atom of the reactive group is more active.
During dyeing, chlorine atoms are replaced by cellulose fibers in alkaline medium and become leaving groups and leave.
The reaction between the dye and the cellulose fiber is a bimolecular nucleophilic substitution reaction (see substitution reaction).
Vinyl sulfone type "The reactive group contained in this type of reactive dyes is vinyl sulfone (D-SO2CH=CH2) or β-hydroxyethyl sulfone sulfate.
During dyeing, β-hydroxyethyl sulfone sulfate ester undergoes elimination reaction to generate vinyl sulfone group in alkaline medium, and then combines with cellulose fiber and undergoes nucleophilic addition reaction to form a covalent bond.
The above two types of reactive dyes are the main reactive dyes with the largest output in the world.
In order to improve the fixation rate of reactive dyes, two reactive groups have been introduced into the dye molecule in recent years, called dual reactive dyes.
In addition to the varieties for cellulose fibers, reactive dyes have also developed varieties for protein fibers (such as silk, wool and other fibers).